#!/usr/bin/python3
# -*- coding: utf-8 -*-

import sys

x1, y1, x2, y2 = map(float, sys.stdin.readline().split())
print(round(((x2-x1)**2 + (y2-y1)**2) ** 0.5, 6))
 import sys sys x1, y1, x2, y2 = map(float, sys.stdin.readline().split()) x1 map(float, sys.stdin.readline().split()) map float sys.stdin.readline().split() sys.stdin.readline().split sys.stdin.readline() sys.stdin.readline sys.stdin sys stdin readline split y1 x2 y2 print(round(((x2-x1)**2 + (y2-y1)**2) ** 0.5, 6)) print round(((x2-x1)**2 + (y2-y1)**2) ** 0.5, 6) round ((x2-x1)**2 + (y2-y1)**2) ** 0.5 (x2-x1)**2 + (y2-y1)**2 (x2-x1)**2 x2-x1 x2 x1 2 (y2-y1)**2 y2-y1 y2 y1 2 0.5 6 x2, y2 = map(float, sys.stdin.readline().split()) map(float, sys.stdin.readline().split()) x2 y2 = map(float, sys.stdin.readline().split()) map(float, sys.stdin.readline().split()) y2 y1, x2, y2 = map(float, sys.stdin.readline().split()) map(float, sys.stdin.readline().split()) y1 x1, y1, x2, y2 = map(float, sys.stdin.readline().split()) map(float, sys.stdin.readline().split()) x1
#!/usr/bin/python3
# -*- coding: utf-8 -*-

import sys

x1, y1, x2, y2 = map(float, sys.stdin.readline().split())
print(round(((x2-x1)**2 + (y2-y1)**2) ** 0.5, 6))

